Various methods of manufacturing steel reinforcing bar have been well-known in the art for many years. Reinforcing bar is vital to the construction of roads, bridges, and the other concrete structures. In the manufacture of reinforcing rod, hot steel stock or rod is typically passed between several pairs of rollers, termed "rolls," driven in opposite directions, which is termed "rolling." Repeated rolling is necessary to give the finished steel reinforcing rod sufficient tensile strength and rolling also aids in descaling, or the removal of surface imperfections on the steel rod. The pair of rolls are usually mounted inside a housing on shafts, and the complete unit is commonly known as "a stand." The steel rod assumes the shape of the roll profile as it passes through the stand. In the case of round steel reinforcing bars, the steel rod must be rolled by alternate stands on opposite sides so that the resulting product is symmetrical.
In a conventional rolling mill layout, all of the stands are arranged on the same axis, and the steel rod are twisted approximately 90.degree. by either twist guides or twist rollers as they enter the next stand. This is termed the twist-method. Use of this method for production of steel rod has often been troublesome, because an incorrect setting of the twist angle, or wear in the twist rollers can prevent the steel rod from entering the next stand in a proper alignment, or at all. Despite attempts to overcome these problems, they remain a major source of downtime. Use of the twist-method to produce steel rod is also problematic in that there is a greater possibility of surface defects resulting from contacts of the steel bar with the twist guides or twist rollers.
The development of the arrangement of stands in alternate horizontal and vertical axes has eliminated many of the inherent shortcomings of the twist-method, especially in the rolling of round products. This arrangement has been commonly adopted by modern-day rolling mills, especially in the production of alloy steel products, where the surface finish of the final product is very critical.
In the production of small diameter round steel reinforcing bar, because of its small cross section and hence light mass per length, very high rolling speeds must be maintained in order to achieve high productivity. However, with higher rolling speeds, the problems associated with twisting of the bar between the stands are amplified. Further problems arise with the collection of the finished steel reinforcing bars after the rolling process at such high speeds, and the collection is usually done by coiling the bars as they leave the rolling process, and thereafter, the steel rod must be straightened by a separate process. At lower speeds, the finished straight rod can be deposited directly onto cooling beds.
Recently, a new method for producing steel reinforcing bar has been developed which involves rolling the steel stock into a profile which is later slit and is further rolled into the required shape and sizes. This is termed the "slit-rolling" method The advantage of this system is that the same productivity can be maintained at half the rolling speeds and hence the finished bars can be delivered straight onto conventional cooling beds. However, the adoption of the slit-rolling method using either the conventional horizontal stand arrangement or the horizontal and vertical stand arrangement still has inherent shortcomings as described below.
FIG. 1 illustrates the typical horizontal stand slit-rolling mill, without showing rod twisting guides or twisting rollers, the base, or the turning means for the rollers. Twisting of the steel rod remains necessary between all stands including between the final two stands 17 and 18. The twisting of each rod emerging from stand 17 is critical because if problems occur on one of the stands, the production on the other stand is interrupted as well, thereby causing a bottleneck in production.
A typical horizontal and vertical slit-rolling mill, without showing rod twisting guides or twisting rolls, or the base, or the turning means for the rolls, is illustrated in FIG. 2. Although the majority of the twisting is eliminated, twisting of the steel rod remains necessary between stands 14 and 15 and from stand 15 to 16. Furthermore, the overlapping of the slitted oval section from stand 17 to 18 involves bending the steel rod at its longer axis on its cross section, which results in the full advantage of the horizontal and vertical arrangement not being realized.